This invention relates generally to liquid chromatography apparatus and, more particularly, to a liquid chromatography pumping system that delivers fluids at precisely metered rates.
Prior fluid pumps used in high pressure liquid chromatography systems have been designed with one or two pistons utilizing spring or gravity loaded ball and seat check valves of very hard material. Each pressuring chamber of such pumps is normally equipped with two such check valves, one on the inlet side and one on the outlet side of the chamber. Typically, the piston of the pump runs in a high pressure sealing system that wears and will leak after some time in service. In addition, prior pumps have been very sensitive to dissolved gas contained in the liquids being pumped. Gas liberated due to reduced pressures during the inlet phase of operation can accumulate in the pumping chamber and will not be expelled through the outlet because of the back pressure present. Consequently, the pump will stop pumping liquid. Other problems are produced by typical hard seat check valves which can be propped open by particulate matter and leak. Also, ordinary inlet valves are opened on an inlet stroke by suction that contributes to undesirable gas generation from the liquid being pumped.
Other problems associated with liquid chromatography systems stem from the fixed mechanical mechanisms used to connect plungers and driving mechanisms in ordinary pumps. The alignment in such pumps is never perfect and results in wear of the plunger and seal material resulting in shortened intervals between replacement of these parts. In addition, pumping losses in prior systems generate heat that increases the temperature of the liquid being pumped and in many applications the increased temperature interferes with required measurements.
In most prior systems, dual piston pumps have been used to minimize pressure pulsation in the liquid flow. However, the two pistons are driven by a single motor or other driving mechanism and undesirable interactions occur when the delivery of liquid is switched from one piston to the other. Many schemes have been developed to vary the speed of the driver to compensate for these interactions, but they can never be eliminated as long as the two pistons are linked.
The object of this invention, therefore, is to provide an improved pumping system that alleviates the problems associated with prior liquid chromatography systems.